Hydraulic circuit



July 31, M RK 2,380,810

HYDRAULIC C IRCUIT Filed July 5, 1941 2 Shets-QSheet 1 Glamor Q July 31, 1945.

G. A. WAHLMARK HYDRAULIC CIRCUIT Filed July 5, 1941,

2 Sheeias-Sheet 2 Patented July 31, 1945 UNITED STATES PATENT OFFICE sm izlflififlim Applicatlz: gill:-

The invention relates to a hydraulic circuit particularly adaptable for use with a machine tool and has as a general object to provide a circuit of new and improved construction.

A more particular object of the invention is to provide a circuit including a motor and new and improved means for braking the motor when the element driven thereby is to be brought to rest.

Another object is to provide a circuit including a motor and means for causing the motor to operate against a high back pressure for rapid deceleration of the motor when it is desired to arrest movement of the elementdriven by the motor. I

Another object is to provide a circuit including a motor, means for maintaining a normal low back pressure on the discharge side of the motor and means providing a high back pressure on the discharge side 01' the motor during'deceleration oi the elementdriven by the motor.

Still another object is to provide a circuit including a variable stroke motor, means for maintaining a normal low back pressure on the dis charge side of the motor and means adjustable to provide a high back pressure during deceleration of the element driven by the motor, the motor stroke being adjusted simultaneously with the adjustment to obtain the higher back pressure to increase the torque of the motor.

Other objects and advantages will become ahparent from the following detailed description taken in connection with the accompanying drawings, in which:

Fig. l. is a diagrammatic view showing a circuit embodying the features oi? this invention. The circuit is shown in running position.

Fig. 2 is a diagrammatic view similar to l, but showing the circuit in braking position.

The circuit shown in the drawings tor purposes of disclosing an exemplary embodiment of the invention comprises generally a. variable displacement motor M, a pump P for supplying operating fluid to the motor, means for controlling the dis-* placement of the motor, and means for controlling the supply of operating fluid by the pump to ternally thereof. One end of the bore I is closed by a screw plug 9 while the other end is closed by a suitable'cap I 0, including a threaded pin l l forming an adjustable abutment for limiting movement of the piston 6 in one direction. The wobbler has projecting radially therefrom a finger orarm l2 which is received in an appropriately formed socket ii in the piston 6, so that shift of the piston varies the tilt of the Wobbler. Herein minimum stroke of the motor pistons is obtained when the piston 6 is shifted to the left, as shown in Fig.1, while an increased stroke is obtained when the piston d is shifted to the right, this stroke being variable to a degree by adjustment of the pin it.

Supply of fluid to shift the piston 6 and thus vary the displacement oi the motor is under the control of a valve means, generally designated it, which will hereinafter be knownas the displacement control valve means. comprises a valve It of the cylinder type reciprocable in a valve bore it having an enlarged portion ill at one end. Spaced inwardly from the ends of the valve are annular srooves it and 2t connected by radial ports ti and it, respectively, with an axial passage til opening only through the lei't end of the valve so as to he in communication with the enlarged portion it of the valve bore. Intermediate the grooves ill and Eli the slveis formed with a reduced portion The hore it has opening thereinto three annular grooves 25, so and the grooves losing equally spaced and spaced to permit bridging oi adjacent grooves by the reduced portion of the valve ill. Groove it is by a conduit 2t; connected to o port 22%? opening to the left hand end of the cylinder ll, while groove 21? is by conduit 3t connected to a port iii opening to the right hand end of the cylinder t. Groove Ed is, will later become more apparent, connected by a conduit lit to the main fluid supply conduit, while the enlarged portion ill of the valve "core is by a conduit til connected to the tank or reservoir it.

The valve it has two operative positions, namely, that shown in Fig. 1 wherein the grooves 26 and M. are bridged, and the other, wherein the valve is shiited to the right to the position shown in Fig. 2, wherein the grooves 26 and ill are bridged. The valve is constantly urged to the second mentioned position namely, that shown This valve means i in Fig. 2, by a light compression spring 88 positioned in the enlarged portion [8 of the valve bore and bearing against the end of the valve so as to urge the same to the right, the extent of movement being limited by abutment of the valve with the end of the valve bore. The valve is shifted to the flrst mentioned position, namely, that shown in Fig. 1, by fluid under pressure which is discharged to the bore through an end port 36. Movement of the valve to the left is limited by a pin 81.

The pump P is of the constant displacement, rotary element type well known in the art. The pump operates when driven by a suitable means (not shown) to draw fluid from the tank 84 through an intake conduit 38, which preferably has a filter or strainer 38 interposed therein, and discharge the fluid under pressure into a main supply line or conduit 40. Governing the-direction. in which fluid discharged by the pump P is supplied to the motor, and hence the direction of operation of the motor, is a directional control valve means generally designated 43. This valve means comprises a valve M 01' the cylinder type reciprocable in a valve bore 45 and having three reduced portions 48, 81 and 48 of equal length. The valve bore 48 has opening thereto flve annular grooves 48, 80, El, 82 and 58, all equally spaced and so spaced that adjacent grooves may be bridged by the reduced portions oi the valve 68. The central groove ill is connected to the supply conduit to, while the grooves 88 and 82 on opposite sides of the groove Eli are. respectively, connected by conduits 88 and 58 to the main motor ports. These latter conduits 58 and 88 serve alternatively as supply or return conduits depending upon whether the valve is in the position shown in Fig. 1 or is shifted to the right, wherein the reduced portion 4i bridges the grooves 58 and Bi.

Also connected to the main supply conduit 48 is a branch conduit 88 leading to a relief valve means, generally designated 8!. The conduit 88 opens through means forming a valve'seat 82 L discharge to a valve bore 88. Cooperating with this seat is a valve 88 urged to seated position by a strong compression spring 88 bearing at one end on the valve and at the other end on a washor 88 seated on an adjusting screw 81. The valve is, by way of example, adjusted to maintain a pressure in the supply conduit 48 up to approximatel 1000 pounds. The pressure maintained by this valve will hereinafter be known as working pressure. The valve bore 88 has opening thereto a single annular groove 88 which is eventually connected to tank through means presently to be described.

Means is provided for governing the supply of eifective operating fluid to the motor and hence there is associated with the main supply conduit 48 a valve means, generally designated 18, which serves as a stop and running valve means. This valve means comprises a valve ll of the cylinder type reciprocable in a valve bore 12. The valve ll hastwo reduced portions 13 and 14 of equal length, and a reduced portion I8 of a length somewhat shorter than the portions 18 and 14. Extending axially of the valve is a bore 18 which, through radial ports 11 and I8 respectively opening to the reduced portions 18 and 18, connects those reduced portions. Formed in the valve bore and opening thereto are four annular grooves 18, 80, 8| and 82. Three of these grooves 18, 88 and 8| are equally spaced and are so spaced that any adjacent two may be bridged by either the reduced portion 18 or the reduced portion 14. The groove 42 is spaced from the groove II and cooperates with the reduced portion ll of the valve. The valve has two positions, namely, that shown in Fig. l, which may be termed the running position, and the position which it assumes when shifted to the extreme right, shown in Fig. 2, which may be termed the stop position or the braking position. Groove 82 is connected with the main supply conduit 40 by a branch conduit 48 which at times (when valve II is shifted to the right as viewed in Fig. 2) in conjunction with the bore in the valve H forms a by-pass around the motor M for the fluid discharged by the pump. At this time the fluid in conduits 48 and 40 is no longer at working pressure but merely at the lower pressure maintained by the back pressure valve means 88. The intermediate groove 88 of the three equally spaced grooves is connected by a conduit 88 to the groove 88 of the directional control valve means, and by a branch conduit 84 to the groove 48 of the directional control valve means to form part of a discharge or return line from the motor.

This discharge or return line also includes a conduit and a pressure opened valve means, generally designated 88, operable at all times to maintain a low back pressure in the return line to steady the normal operation of the motor and to provide a convenient source of control fluid at a suitable pressure. The conduit 88 connects at one end to the groove 18 oi valve means 18 and at the other end discharges to one end of the bore 81 of valve means 88. Reciprocable in the bore is a valve 88 of the piston type which is urged toward the end of the bore through which the conduit 88 opens by a light compression spring 88 bearing at one end against the valve and at the other end against a washer 88 seated on an adjusting screw 95. Opening through the side walls or the bore are widely spaced annular grooves 82 and 93. Communication between the conduit 85 and the groove 82 is controlled by the valve 88, but the groove 83 is constantly open to the valve bore 81. The return or discharge line of the circuit is completed by a conduit 84 leading from the groove 82 to the tank 84 and a branch conduit 88 leading from the groove 88 to the conduit 84. The back pressure valve means, by way of example. is adjusted to maintain up to 60 pounds per square inch pressure. To permit return to tank of any fluid flowing past the relief valve means 8!, a conduit 88 is conncc'fed'between the groove 88 and the conduit 88.

It is a feature of this invention to provide unique and improved means for rapidly decelerating the motor and the element driven thereby. Herein this is accomplished by compellins the motor to discharge fluid against a high back pressure during such deceleration. The means for accomplishing this function herein takes the tom of a pressure opened valve means, generally designated 81. similar to the back pressure valve means 88 but capable of maintaining substantially higher back pressures. This valve means will hereinafter be termed braking valve means, in order more readily to distinguish the same from the low back pressure, valve means 88. This braking valve means comprises a valve 88 of the piston type reciprocable in a valve bore 88. Opening to the valve bore 88 at one end is a port I88. while opening through the side walls of the bore 81 near the ends thereof are widely spaced annular grooves "I and I82. Communication between the port I" and the groove III, is controlled by the valve 00. Groove I02, however, is not controlled by the valve 03. but is in all positions of the valve open to the bore 99. The valve 98 is urged in a direction to cut of! communication between the port I and. the groove IOI by a strong compression spring I03 hearing at one end against the end of the valve and atthe other end on a washer I04 seated on an adjusting screw I05. The pressure at which the valve means will open may thus be adjusted by the screw I05 and is herein, for exemplary purposes, considered adjusted to maintain a pressure of 1000 pounds per square inch.

In order that this valve means may be interposed in the return line of the circuit during deceleration of the motor, but not'during normal operation, its connections to the circuit are governed by the running and stop or braking valve means I0. Thus port I00 is by a conduit I06 connected to the groove 3|, while groove I9 of the valve means I0 is by conduit I01 and a branch conduit I03 connected respectively to the grooves IM and I02. It is to be noted that the valve means 91 is thus connected in the return line in advance of the low back pressure valve means 86, and also in advance of the point of discharge of the by-pass line to the return line. The valve 90 is formed with a small bleed orifice I09 in its closed end, which orifice serves to permit manual operation of the motor when the' valve TI is in stop or braking position, as will later be more fully described.

It is also a feature of this invention to aid and abet the deceleration of the motor by the braking valve means to change the tilt of the Wobbler, so as to obtain maximum torque of the motor during such deceleration. To that end, the valve II is shifted hydraulically and with the valve means I5 is under the control of .a common pilot valve means, generally designated II4. This valve means comprises a valve II 5 of the cylinder type reciprocable in a valvebore II6. At one end the valve is formed with an annular groove III which, through a radial port H0, communicates with an axial bore I I9 opening only through the end of the valve opposite that carrying the groove III. Spaced from the groove III is a substantially Wider groove formed by a reduced portion I of the valve. Opening to the valve bore are three annular grooves I2I, I22 and I23, all equally spaced and so spaced as to permit the bridging of any two adjacent grooves by the reduced portion I20 of the valve. The valve is intended to be suitably actuated, most likely manually, and has two positions, namely, that shown in Fig. 1, which may be termed the start or running position, and that shown in Fig. 2, which may be termed the stop or braking position.

Control fluid is derived from the return conduit 05, such fluid at all times being maintained at a suitable pressure by the back pressure valve means 00. Such control fluid is supplied to the pilot valve means I I4 through a conduit I20 connected at one end to the return conduit 85 and at the other end to the groove I22 which is the intermediate one of the three grooves I2I, I22 and I23. Groove I2I is in turn connected to the port 30 of the valve means I5 by a conduit I and to the right hand end of the bore I2 of the valve means I0 by a branch conduit I23. The left hand end of bore I2 is by conduit I'2I connected to the groove I23 and a conduit I20 connects the end of the bore II6 to the tank. It will thus be seen that the valve II and the valve It will be shiftedsimultaneously and that thus the Wobbler of the motor M will be tilted to obtain the maximum motor stroke simultaneously with the connection of the braking valve means in the return circuit.

The directional control valve means 43 is also hydraulically shifted and is, therefore, under the control of a reversing pilot valve means, generally designated I30. This valve means is identical with the valve means I I4 comprising a valve I3I of the cylinder type reciprocable in a valve bore I32. The valve is formed with an annular groove I33 near one end which, through a radial port I34, communicates with an axial bore I35 opening only through the end of the valve remote from the groove I33. Intermediate its ends the valve is formed with a reduced portion I33. Opening to the bore are three annular grooves I3'I, I38 and I39, the intermediate groove I30 being by conduit I00 connected to the conduit I24. Grooves I31 and I30 are by conduits HI and I42, respectively, connected to the right and left hand ends of the bore 05. A conduit I33 connects the end of the bore I32 to the tank.

For a more ready understanding of the invention, the operation of the circuit will now be described briefly. The features of the invention will most readily be understood and appreciated if the operation is considered in transition from a condition of the circuit in which the motor is operating normally t one in which the motor will be at rest. Thus, let it be assumed that the motor is already running, in which case the various valve means will assume the positions shown in Fig. 1. More particularly, the start and stop pilot valve means I I4 will be in its upper or start position wherein control fluid is supplied to the right hand ends of both the displacement control valve means I5 and the running-braking valve means I0. The valve I6 will then be shifted to the left against the stop 31, thereby bridging the grooves 28 and 21 and permitting the supply of pressure fluid to the right hand end of cylinder 8. This will shift the piston 6 to the left and thus will, as previously mentioned, place the Wobbler in such position as to produce minimum stroke of the motor pistons, thereby giving high speed operation at low torque of the motor. The fluid supplied to the right hand end of the valve means I0 will shift the valve II to the left, thereby blocking the groove 82 closing the by-pass line 40 and bridging the grooves I9 and completing a return line which does not include the braking valve means 91. The return circuit does, however, include the back pressure valve means 86 which maintains at all times a low back pressure. This constant low back pressure, first of all, steadies the operation of the motor M in that it resists tendencies on the part of the driven element to overrun, and, secondly, provides a. source for the control fluid. Under this condition, the directional control valve means 43 may be shifted back and forth under the control of the reversing pilot valve means I30 to reverse the operation of the motor, but no further change takes place with such reversal of motor operation.

If now the start-stop pilot valve means H0 is shifted downwardly to its stop position, shown in Fig. 2, the improved and unique circuit arrangement herein provided will come into play quickly to decelerate the motor and the element driven thereby. With this shift of the valve lit to its stop position, grooves I22 and I23. are now bridged, thereby supplying control fluid to the left hand end of the valve bore I2. At the same time, groove H1 now registers with groove Hi to connect the conduit I25 to tank, thereby permitting the valve H, under the influence of the control fluid supplied to its left hand end, and the valve l6, under the influence of the spring 35, to be shifted to the right to the position shown in Fig. 2. In this position, the reduced portion of the valve ll registers with the groove 82, thereby connecting the branch conduit 40 to the return conduit 85 completing the by-pass passage around the motor, and permitting the fluid discharged by the pump to discharge to the tank through the back pressure valve means 86. The grooves 80 and 8| are now bridged, thereby connecting the braking valve means 91 in the return line of the circuit. The fluid discharged by the motor M now must overcome the valve means 91 and thus there will be set up a high back pressure counteracting the inertia tendency of the motor and the element driven by the motor to continue to operate in the same direction. The circuit arrangement here shown has the additional advantage that though, in the stop or braking position of the valve H, fluid supplied by the pump is not effective to drive the motor, yet it is not completely out off from the motor, but still may be drawn into the motor to maintain operation with the cylinders full of fluid and the piston held against the Wobbler.

With the valve "5 shifted to the right the grooves and 26 will now be connected while groove 21 will, through groove 20, be connected to tank. Thus fluid under pressure will be supplied to the left end of the cylinder 8, thereby shifting the piston 6 to the right into abutment with the adjusting screw II. This will tilt the Wobbler so as to increase the stroke of the pistons and thereby increase the torque of the motor. As a consequence, the high back pressure in conjunction with the increased torque of the motor will quickly bring the motor and the element driven thereby to rest.

In this condition, the motor will remain at rest until, through shift of the start-stop pilot valve means, the valve means 10 and the valve means l5 are again shifted in the opposite direction. Though the motor is at rest, it may be manually actuated for adjustment purposes. Such manual actuation is permitted because of the bleed orifice formed in the end of the piston valve 98. This bleed orifice permits fluid to flow from the conduit 83, grooves 80 and 8| which are now bridged by the reduced portion 14, conduit I06, groove I02, and conduits I08 and I0! to the groove 19 at a rate at which fluid is displaced by manual operation of the motor M. Any excess of fluid accumulating in the casing of the motor overflows to tank through conduit I44.

I claim as my invention:

1. In a hydraulic circuit, a motor, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a high back pressure valve means, and means operable in eflect to exclude said back pressure valve means from the return line and cause fluid from said pump to be supplied to said motor at working pressure or alternatively to discontinue the supply of fluid at working pressure to said motor and to interpose said back pressure valve means in the return line of the circuit.

2. In a hydraulic circuit, a motor, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a by-pass line connected between said supply line and said return line, a fluid pressure opened valve means, and control valve means having a plurality of positions in one of which the by-pass line is closed and the pressure opened valve means excluded from the return line and in another of which the by-pass line is open and said pressure opened valve means is interposed in the return line in advance of the connection therewith of the by-pass line.

3. In a hydraulic circuit, a motor, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a first fluid pressure opened valve means permanently connected in the return line of the circuit, a second normally closed valve means adapted to be opened by the pressure of the fluid flowing therethrough, said second valve means operating at a substantially higher pressure than said first valve means, and means for alternatively interposing said second valve means in or disconnecting the same from the return line of the circuit.

4. In a hydraulic circuit, a motor, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a first fluid pressure opened valve means permanently connected in the return line of the circuit, a second fluid pressure opened valve means, said second valve means operating at a substantially higher pressure than said first valve means, and a control valve means having a stop and running position, said control valve means in running position disassociating said second valve means from the circuit and in stop position connecting the pump to the return line and interposing said second valve means in the return line in advance of the point of connection of the supply line therewith.

5. In a hydraulic circuit, a variable displacement motor, a pump for supplying operating fluid at working pressure to said motor, valve means governing the supply of fluid by the pump to the motor, and simultaneously operable hydraulic means governing the displacement of said motor to obtain maximum displacement of said motor when the supply of fluid at working pressure is discontinued.

6. In a hydraulic circuit, a variable displacement motor, hydraulically actuated means for varying the displacement of said motor, a pump for supplying operating fluid to said motor, valve means having a stop position and a running position governing the supply of fluid by said pump to said motor, and means governing said hydraulically actuated displacement varying means to adjust said motor to maximum displacement when said valve means is in stop position.

7. In a hydraulic circuit, a variable displacement motor, hydraulically actuated means for varying the displacement of said motor, a first hydraulically controlled valve means governing said displacement varying means, a pump for supplying fluid to said motor, a second hydraulically actuated valve means having a stop position and a running position governing the supply of fluid by said pump to said motor, and pilot valve means governing said first and second valve means to obtain maximum motor displacement when said second valve means is shifted to stop position.

8. In a hydraulic circuit, a variable displacement motor, means governing the displacement of said motor, a pump for supplying operating cuit and simultaneously actuate said displacement governing means to obtain maximum displacement of the motor.

9. Ina hydraulic circuit, a variable torque motor, means governing the torque of said motor,

a pump for supplying operating fluid to said motor, a, supply line leading from said pump to said motor, a return line leading from said motor, a fluid pressure opened valve means, control valve means having a plurality of positions in one of which the pressure opened valve means is excluded from the return line and fiuid from said pump caused to be supplied to said motor at working pressure and in another of which the supply of fluid to the motor at working pressure is cut off and said pressure opened valve means is interposed in the return line, and means for simultaneously controlling said control valve means and said torque governing means to obtain maximum torque when said valve means is in its last mentioned position and minimum torque when said valve means is in its first mentioned position.

10. In a, hydraulic circuit, a variable displacement motor of the Wobbler type, hydraulically actuated means governing the displacement of said motor, a first hydraulically controlled valve means governing said displacement varying means, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a by-pass line connected to said supply line, a fluid pressure opened valve means, a second hydraulically actuated valve means having a plurality of positions in one of which the bypass line is closed and the pressure opened valve means excluded from the return line, and in another or which the by-pass line is connected to the return line and said pressure opened valve means is interposed in the return line in advance of the connection therewith of the bypass line, and pilot valve means exercising common and simultaneous control over said first and second valve means to obtain maximum displacement of said motor when said fluid pressure opened valve means is connected in the return line.

11. In a hydraulic circuit, a, variable displacement motor of the Wobbler type, hydraulically actuated means governing the displacement of said motor, a first hydraulically controlled valve means governing said displacement varying means, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a by-pass line connected to said supply line, a fluid pressure opened valve means, a second hydraulically actuated valve means having a plurality of positions in one of which the bypass line is closed and the pressure opened valve means excluded from the return line, and in another of which the by-pass line is connected to the return line and said pressure opened valve means is interposed in the return line in advance of the connection therewith of the by-pass line, pilot valve means exercising common and simul taneous control over said first and second valve means to obtain maximum displacement of s-aid motor when said fluid pressure opened valve means is connected in the return line, a conduit leading from said return line to saidpilot valve means to supply control fluid thereto, and a second low back pressure valve means permanently interposed in the return line beyond the point of connection thereto of said last mentioned conduitto maintain fluid at suitable control pressure.

12. In a hydraulic circuit, a motor, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a by-pass line connected to said supply line, a fluid pressure opened valve means, and control means having a plurality of positions in one of which the by-pass line is closed and the pressure opened valve means excluded from the return line, and in another of which the by-passline is open and said pressure opened valve means is-interposed in the' return line.

13, In a hydraulic circuit, a motor, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, a first fluid pressure opened valve means, a second fluid pressure opened valve means, said second valve means operating at a substantially higher pressure than said first valve means, and a control valve means having a stop and a running position governing the supply of fluid at working pressure to said motor, said first fluid pressure opened valve means being connected in said return line when said control valve is in running position, and said control valve being operable when in stop position to connect said second fluid pressure opened valve means in said return line and when in running position to disconnect the same therefrom.

14. In a hydraulic circuit, a variable torque motor, means governing the torque of said motor, a pump for supplying operating fluid to said motor, a supply line leading from said pump to said motor, a return line leading from said motor, means for creating back pressure in said return line, and means operable alternatively to reduce the pressure of the liquid supplied to said motor and simultaneously to increase the torque 01' said motor and the back pressure, or to increase the pressure of the fluid supplied to said motor and simultaneously to decrease the torque of said motor and the back pressure.

GUNNAR A. WAHLMARK. 

